1. Field of the Invention
The present invention relates to a method and apparatus for producing and detecting an image of a topographic surface such as a fingerprint for optical viewing, or storage in a recording medium such as photographic film, a hologram, or computer storage means. The topographic image may be independently analyzed or compared with previously recorded topographic data. Such methods and apparatus are used, for example, for personal identification in the criminology and access control fields.
2. Description of the Related Art
Examination of the fingerprints or other biometric features of an individual is a well known technique to establish a person's identity. In the past, fingerprints were recorded by applying ink to the finger and then rolling the finger on a piece of paper. Agencies then maintained these originals, or photocopies or photographs of the originals. Later comparison of these archives with a live or latent fingerprint could prove to be quite tedious and time consuming. More recently, methods have arisen to create fingerprint images which can be captured directly electronically for storage and/or analysis by a computer, or photographically for storage on film.
Many methods have been proposed for optical detection of fingerprints and other topographic biometric features such as footprints and palmprints. Most of these methods utilize optical systems, typically incorporate a prism or beamsplitting apparatus, and operate on the principle of frustrated total internal reflection. Such systems are necessarily bulky, cannot detect certain skin detail information, such as valley or pore detail, or require expensive optical components. In addition some prior art systems suffer from distortion, poor signal to noise ratio, aberrations, lack of contrast, and/or lack of resolution of finger detail information. There are many patents which describe variations of optical systems wherein illuminating light is directed into a prism. The basic common concept as applied, for example to inkless fingerprint detection, involves illuminating one side of a prism with light and pressing a finger onto another surface of the prism, usually the hypotenuse. A fingerprint image, formed by frustrated total internal reflection, is created where the finger meets the prim. Light passing out of the prism containing the fingerprint image is then captured by an image detection system. For example, in U.S. Pat. No. 3,174,414, J. Myer describes apparatus for recording fingerprints using photochemical or xerographic means separately or in combination with photographs. This U.S. Patent shows various means of creating a fingerprint image by the principle of total internal reflection, using a prism, and other optical system parts to relay the fingerprint image. Many other such examples of prism-based systems exist in the prior art, and can be found such as U.S. Pat. No. 3,482,498 to L. Becker and U.S. Pat. No. 3,947,128 to Z. Weinberger, et. al.
Other prior art systems illuminate and/or view the finger directly, without using the principle of total internal reflection. One such system is described in U.S. Pat. No. 3,138,059 to W. White. U.S. Pat. No. 5, 177,802 to Y. Fujimoto, et. al. describes a system which uses a light guide plate having a through hole, so that the finger is in air, and light traveling through the light guide exits the light guide near the hole to illuminate the finger. The finger image is captured by a detection system directly opposite the finger. In another system, the finger rests on the light guide surface and operates by frustrated total internal reflection of the illuminating light traveling through the light guide. A third system is described which does not use a light guide, but uses linear light sources such as fluorescent tubes placed near the "belly" of the finger to be imaged, and a detection system to image the finger directly. In embodiments, the finger is illuminated directly via light emerging from the light guide, the light strikes the finger at an angle, limiting uniformity of illumination and contrast. The embodiment utilizing fluorescent tube illumination additionally suffers from bulkiness and direct lamp light reaching the detector, reducing the signal to noise ratio of images produced using this system.
Other types of systems involving comparison and scanned illumination have been described. U.S. Pat. No. 3,511,571 describes a method wherein the surface of the finger is flooded with light. The light reflected from the finger may be passed through a transparency of a previously recorded fingerprint for direct comparison. U.S. Pat. No. 3,200,701 describes a system wherein light is scanned onto the finger and the reflected light produces an output which can yield a fingerprint image. U.S. Pat. Nos. 3,864,042 and 4,003,656 also describe systems for illuminating a finger with a scanning light beam.
Various methods have been proposed utilizing holograms as part of the fingerprint illumination and detection system. U.S. Pat. No. 5,109,427 describes a fingerprint recognition device which uses collimated laser light which illuminates the finger through a tetragonal prism. A hologram is used to shift the axis of the fingerprint image to a second optical axis. An objective lens then projects the fingerprint image to a CCD camera.
In the paper entitled "Real-time fingerprint sensor using a hologram", Applied Optics, Vol. 31, No. 11, p.1794ff, and in U.S. Pat. No. 4,728,186 entitled `Uneven Surface Date Detection Apparatus`, S. Eguchi, S. Igaki, et. al. describe a system wherein laser light illuminates a finger directly through, or via waveguiding through a substrate. The scattered light reflected from the finger travels through the substrate, which acts as a light pipe. A plain grating type hologram attached to the substrate allows rays with the proper angle to exit the substrate, wherein a lens then images the exiting light containing the fingerprint information to a CCD camera or other detector. Other embodiments include a hologram to direct the light to the finger, but the finger image still travels by total internal reflection to be output to a detection system located along a different optical axis from the finger. In the Eguchi system, a hologram is primarily used to extract the fingerprint information after the information has traveled through a waveguide. The input light path to the finger and the output light path to the detection system are necessarily along different optical axes. Expectedly, this prior art system suffers from loss of information due to imperfections in the waveguide, or damage to the information in the form of additional noise, distortions or aberrations due to its travel through the waveguide and/or the hologram extracting means. In addition, the geometry of this prior art system limits its ability to be extremely compact.
Other prior art systems use a hologram, but for different purposes. For example, in U.S. Pat. No. 4,053,228, a fingerprint is compared against a fingerprint which is stored on a hologram.
U.S. Pat. No. 3,430,300 to H. Ruell describes a means for forming a latent topographic relief of a finger pattern. It uses a deformable polymer which illuminated through its edge and upon which a finger is pressed. The deformation caused by the finger causes frustrated total internal reflection which redirects the illuminating light at the points of frustration to the output face of the substrate. This system does not use a hologram, requires a deformable surface, and, operates on the principle of total internal reflection.
Thus, there is a great need in the art for an improved method and apparatus for producing high-contrast images of the surface topography of objects, such as finger and foot surfaces, while avoiding the shortcomings and drawbacks of prior art systems and methodologies.